Possibly caused by e6dd624baeca16efe462e3938969a72c9ef4ed1e / T29540?

The behavior change is also on LTR wikis but there it is now left aligned instead of centered.

I think now the behavior is consistent. With and without mode="packed" the images are left/right aligned. When you want to have centered images you can add style="margin:auto".

this broke some page layouts in hebrew wiki.

Out of curiosity, could you give any examples of affected pages?

After some testing I'm inclined to revert e6dd624baeca16efe462e3938969a72c9ef4ed1e and rethink T29540, it's causing the 'packed' gallery JS resizing to not work entirely correctly for small galleries (they don't grow to fit the page width, because their width is now limited). Same issue affects 'slideshow' galleries.

In T149412#2757312, @matmarex wrote:

this broke some page layouts in hebrew wiki.

Out of curiosity, could you give any examples of affected pages?

for example:
https://he.wikipedia.org/wiki/%D7%90%D7%A8%D7%A6%D7%95%D7%AA_%D7%94%D7%91%D7%A8%D7%99%D7%AA#.D7.A4.D7.90.D7.95.D7.A0.D7.94_.D7.95.D7.A4.D7.9C.D7.95.D7.A8.D7.94

this was nicely centered 3 over 3.

this search query will give you nice examples

In T149412#2757440, @matmarex wrote:

After some testing I'm inclined to revert e6dd624baeca16efe462e3938969a72c9ef4ed1e and rethink T29540, it's causing the 'packed' gallery JS resizing to not work entirely correctly for small galleries (they don't grow to fit the page width, because their width is now limited). Same issue affects 'slideshow' galleries.

I can confirm. packed galleries with one line of images with a width between 66% to 100% of the whole width get not resized anymore. I think this can be solved and should be solved in the packed gallery JavaScript code. The JavaScript code should use the whole width instead of the intrinsic width.

Change 319302 had a related patch set uploaded (by Bartosz Dziewoński):
Revert "Gallery: Use intrinsic width for gallery to center caption"

https://gerrit.wikimedia.org/r/319302

Change 319303 had a related patch set uploaded (by Bartosz Dziewoński):
Revert "Gallery: Use intrinsic width for gallery to center caption"

https://gerrit.wikimedia.org/r/319303

Change 319304 had a related patch set uploaded (by Bartosz Dziewoński):
Revert "Gallery: Use intrinsic width for gallery to center caption"

https://gerrit.wikimedia.org/r/319304

Reverted, and backporting to:

• MW 1.28 (soon to be released)
• MW 1.29.0-wmf.1 (being deployed to Wikimedia wikis this week)

Change 319302 merged by jenkins-bot:
Revert "Gallery: Use intrinsic width for gallery to center caption"

https://gerrit.wikimedia.org/r/319302

Change 319303 merged by jenkins-bot:
Revert "Gallery: Use intrinsic width for gallery to center caption"

https://gerrit.wikimedia.org/r/319303

Change 319304 merged by jenkins-bot:
Revert "Gallery: Use intrinsic width for gallery to center caption"

https://gerrit.wikimedia.org/r/319304